Various arrangements are known in the prior art for scanning printing such as that contained on a label. Some of these devices take their reference and sample signals from a video camera. The images are stored in a computer's random access memory wherein comparisons are made between the reference and sample images by "template matching" tailored to the nature of the inspection being performed. While most of these systems are satisfactory for the purposes for which they are designed, in general they are not suitable for the inspection of compact disc labels, owing to the nature of the labels and their reflective diffraction grating substrates. In most instances, moreover, they are not as sensitive as is desired. Most of them inspect for missing ink but fail to make any provision for inspection with reference to added or superfluous ink.